U-M Physicist Xiaoming Mao and collaborators Qian Chen, University of California, Berkeley and Steve Granick, University of Illinois are researching a burgeoning new field called self-assembly which focuses on ways to obtain new ordered structures through the spontaneous assembly of designed building blocks of natural or engineered materials. Her team has constructed an analytic theory explaining the self-assembly of open lattices.

The team studies open lattices, which are structures with a large amount of open spaces periodically distributed between the building blocks. These holes are similar to the sizes of typical biological cells and also to the wavelength of visible light.

Close-packed structures and small clusters of self-assembly have been well-studied and have already been obtained using simple spherical particles. In contrast, spatially open, but also ordered structures have only very recently been discovered and are not yet understood.

Professor Mao and her research team’s predictions agree well with the new measurements of the self-assembled structures. Counter intuitively, they found that entropy, which is usually associated with fluctuations and disorder, plays the essential role of stabilizing and selecting open lattices.

Professor Mao’s theory leads to great simplifications in the self-assembly of these open lattices, and her team is working on novel experimental designs to realize more open structures. These designs are considerably simpler than previous proposals and are much easier to realize using current fabrication techniques, thus opening the door to a rich variety of novel self-assembled open structures. The resulting open structures may lead to a variety of applications in fields such as mechanical engineering, optics, and medicine. Examples include materials that can immediately change color upon a small change in the stress or magnetic field. Another possibility for self-assembly is “holographic materials” in which the interior deformations are completely determined by highly precise manipulations on the surface of the sample.

The link to Professor Xiaoming Mao's recent Nature Materials paper can be found here.